Why does the age of a child effect what he / she likes to watch?

Well, for one, knowledge plays a big part in that. I highly doubt you would want a four year old child to watch Texas Chainsaw Massacre. Then there is interest. When you were four you probably wanted to watch My Little Pony or Cars. Now, you most likely want to watch an anime or two. Then there are the kids who think they have to be cool by watching what everyone else watches at their age.